1. Field of the Invention
The present invention relates to an endoscope including an illumination section and an image pickup section with a wide view angle.
2. Description of the Related Art
In recent years, endoscopes have been widely used in the medical field and the like. With an endoscope, an organ or the like in a body cavity can be observed by inserting an elongated insertion section into the body cavity, for example, and various kinds of treatment can be made by using a treatment instrument inserted into a treatment instrument insertion channel in accordance with necessity. Further, a bending section is provided at a distal end of an insertion section, and the observation direction of an observation window at a distal end portion can be changed by operating an operation section of the endoscope.
In the endoscope, an optical unit for image pickup including an objective optical system is placed at the distal end portion, and an illumination optical system to be a radiation section of an illumination light source is placed in the vicinity adjacent to the objective optical system. Like this, in the endoscope in which the objective optical system and the illumination optical system are adjacent to each other, illumination light directly enters an objective lens, or intense reflection light from an object enters the objective lens at the time of close observation or the like, and harmful light beams may be photographed, which exerts an adverse effect on an endoscope image, such as halation in which a part of the image becomes white and vague, and lens flare which is the phenomenon in which circular or hexagonal light appears on the a screen by the internal reflection of the lens.
As the countermeasures against such harmful light beams due to illumination, for example, Japanese Patent Application Laid-Open Publication No. 2001-258823 discloses the endoscope in which a plurality of illumination optical systems constituted of wide distribution light and narrow distribution light with the radiation light quantities changed are placed in the periphery of the objective optical system.
Further, some of the conventional endoscopes include wide view angles of, for example, 140° or more at which an endoscope image in a wider range can be photographed than with the conventional view angle of about 120°. In order to realize such a wide view angle, a convex meniscus lens is sometimes used for the objective optical system exposed to the distal end portion of the endoscope. Further, in the illumination optical system, an effective illumination range in which an endoscope image range with a wide angle can be sufficiently illuminated is set.